This invention relates to a radial ply pneumatic tire and to a cylindrical carcass 10 for the pneumatic tire as an intermediate article of manufacture. The carcass 10 in its unvulcanized state is formed into a cylindrical shape at a tire building station and is a subassembly of a radial ply pneumatic tire. The invention is described in relation to a radial ply passenger tire, but it is applicable to light truck medium truck, agricultural, off-road and other radial ply tire constructions.
Historically, the pneumatic tire has been fabricated as a laminate structure of generally toroidal shape having beads, a tread, belt reinforcement and a carcass. The tire is made of rubber, fabric, and steel. The manufacturing technologies employed for the most part involve assembling the many tire components from flat strips or sheets of material. Each component is placed on a building drum and cut to length such that the ends of a component meet or overlap creating a splice.
In the first stage of assembly the carcass would include one or more plies, and a pair of sidewalls, a pair of apexes, an innerliner (for a tubeless tire), a pair of chafers and perhaps a pair of gum shoulder strips. Annular bead cores can be added during this first stage of tire building, and the ply or plies can be turned around the bead cores to form the "ply turnups."
The carcass components (excluding the bead cores) would be either "butt spliced" or "lap spliced." A butt splice has the component ends joined but not overlapped, a lap splice has overlapping ends.
This intermediate article of manufacture would be cylindrically formed at this point in the first stage of assembly. The cylindrical carcass is expanded into a toroidal shape after completion of the first-stage of tire building that results in such cylindrical intermediate article of manufacture. Reinforcing belts and the tread are added to the intermediate article during a second stage of tire manufacture, which can occur using the same building drum or workstation.
During the expansion of the carcass, tensile stresses are imposed on the spliced and uncured components of the tire carcass.
In the case of plies, lap splices were preferred because the splice remained intact whereas butt splices would tend to open or fail. Even with the good adhesion of the lap splice the cords adjacent the splice tended to be stretched compensating for the overlapped two layers of cords at the splice. This localized stretching creates a non-uniformity that is readily visible under x-ray or ultrasonic display.
The tire builder, in order to prevent the creation of tire uniformity problems has historically insured that the splices of the various layers of components were not circumferentially aligned. This non-alignment of splice joints was believed to improve the carcass overall durability, as measured by the ultimate burst strength of the tire. Tire engineers also have believed that tire uniformity could be improved if these discontinuities were deliberately circumferentially spaced around the carcass.
The subject matter of this patent application completely reverses this conventional wisdom as it relates to carcass construction. The carcass is manufactured with numerous components having a common splice line. The tire carcass built according to the present invention can actually increase the tire burst strength while reducing splice-related non-uniformities.